The invention relates to a method and a device for lacquering or coating of a substrate by means of a capillary channel. When the following text in explaining the invention, to simplify matters, only speaks of lacquering, respectively, of lacquering processes, coating, respectively, coating processes with appropriate fluids, i.e. with appropriate lacquers or appropriate coating fluids, are meant also.
In the field of thin layer technology, especially for the production of LCD monitors, of masks for semi-conductor production, semi-conductor substrates or ceramic substrates etc. often the problem is encountered to provide rectangular or round plates with a uniform layer of lacquer or other initially liquid media, for example, with color filters, photo lacquers, or with special protective layers. In accordance with current engineering practices for lacquering the plates are horizontally attached to a turntable. To the center point of the plate a certain quantity of lacquer is dripped from above by means of a nozzle. Then the turntable is rotated. Due to centrifugal forces the lacquer is distributed on the substrate during rotation ("spin coating"). By this a large portion of the lacquer is spun across the rim of the substrate. The achievable uniformness of the layer thickness depends on the magnitude of the rotation acceleration, the rotation speed, as well as on the viscosity of the lacquer.
Difficulties with respect to the uniformness of the lacquer thickness on rectangular, plate-shaped substrates are encountered with this known process especially in the area of the rims of the substrate. In these areas commonly strips of greater lacquer thickness, i.e., so-called lacquer bulges are observed. This causes a substantial reduction in the uniformness of the lacquer thickness.
In order to collect the lacquer which is spun across the rim of the substrate, such lacquering turntables are commonly mounted within a kind of container, for example, see DE-GM 91 034 94. During the lacquering process spun-off lacquer may splash back onto the surfaces of the substrate. This is disadvantageous for the further processing of the substrate. Moreover, with this known method up to more than 90% of the applied lacquer quantity is spun over the rim of the substrate; this excess lacquer can only be reused at very high expenditure/technical resources. The size of the plates that can be lacquered, respectively coated, has an upper limit. Furthermore, small particles may get ground off and released from the rotating parts of such devices, deposit on the surfaces of the plates, and interfere with the subsequent processes. Moreover, during the spinning operation, lacquer hits the edge of the substrate, and this can lead to problems in the subsequent processes. Furthermore, the entire construction and the drive of such a turntable are complicated and expensive.
An improvement of lacquering and coating processes was achieved by a device for lacquering and coating of plates (PCT/DE 93/00777) with which the lacquering, respectively, coating liquid--in the following called fluid--is applied to the downwardly facing surface of the substrate from below by means of an open channel that is narrowed down to a capillary slot. The substrate is guided across the channel at a constant speed. The channel is formed in such a way that it acts as a capillary tube and thus supplies the lacquer automatically and at a particularly constant speed. The capillary action is achieved by the channel being only, for example, less than 0.5 mm wide. As a result of the capillary action the fluid automatically and at a constant speed rises within the capillary slot, against the force of gravity, and flows out at its outlet opening. Above the slot the lacquer stream contacts the surface that is to be coated in a narrow line and is deposited on this surface as a uniform layer while the substrate is moved relative to the outlet opening.
Thus, the lacquering, respectively, coating process is carried out by combined use of capillary action and adhesive action. With this device the uniformness of the thickness of the lacquer layers, particularly on rectangular substrates, can be improved, and the required lacquer quantity decreases. It can have a disadvantageous effect on the operation of the device that the fluid, in longer intervals between the single lacquering, respectively, coating processes begins to dry or dries out in the area of the outlet opening of the capillary slot. This can have a very disadvantageous effect on the subsequent lacquering, respectively, coating process. Furthermore, it can also be disadvantageous that, due to the adhesive action at the end edge of the substrate that is to be lacquered, respectively, to be coated, an undesired bulge of lacquering or coating material is created.
An object of the present invention is to provide a new device and a new method for lacquering and coating of substrates.